Artery sizes Arteries come in a variety of sizes. The largest artery of the body is the aorta, which begins at the heart. As they move further from the heart, arteries branch off and become increasingly smaller. The smallest arteries are called arterioles. Arterioles connect to capillaries, which are the smallest blood vessels and are where the exchange of oxygen, nutrients, and waste occurs between the blood and the cells of the body. After this exchange occurs, the blood enters the venous system, where it travels back toward the heart.